Scalar target fixes.

Don't issue warnings about all instances writing to the same location if
there is only one program instance in the gang.

Be sure to report that all values are equal in one-element vectors in
LLVMVectorValuesAllEqual().

Issue #166.

llvmutil.cpp

@@ -597,6 +597,9 @@ LLVMFlattenInsertChain(llvm::InsertElementInst *ie, int vectorWidth,
 bool
 LLVMVectorValuesAllEqual(llvm::Value *v, int vectorLength,
                          std::vector<llvm::PHINode *> &seenPhis) {
+    if (vectorLength == 1)
+        return true;
+
     if (llvm::isa<llvm::ConstantAggregateZero>(v))
         return true;